Tube vs Tire sizes

I have been gravitating toward larger tires on my road bike - going from
23s to 25's, and I've just ordered some 28's. I've been generally
trying to use the smallest tube for a given tire. Does anyone know if
I can use a tube rated for 18-25mm on a 28? All tires and tubes in
question are Contis (tires are Ultra 2000).

Also, I'm a bit concerned with tire clearance on my bike frames. I
don't have much with 25's right now (tire to seat tube in back and tire
to fork), and in theory, the 28's should have a larger diameter. I
guess I'll find out for sure when I get the tires, but I was wondering
if this diameter varies a lot (I would have to think it does vary
some).


--
Jesse Falsone

Jesse Falsone wrote:
I have been gravitating toward larger tires on my road bike - going from
23s to 25's, and I've just ordered some 28's. I've been generally
trying to use the smallest tube for a given tire. Does anyone know if
I can use a tube rated for 18-25mm on a 28?

You can, and I used to do this sort of thing. However, the tube will be
stretched thinner, and will become easier to puncture. I eventually
came to the realization that the teeny weight differnece wasn't worth
the additional hassle.

You'll likely need to "top off" your tire pressure more often, again due
to the tube being stretched thin. If you neglect this, you'll suffer
"snake bite" pinch flats.

Tube sizing is not critical, but it is better to have the tube a
reasonably close fit to the tire in use.

Sheldon "Weight Isn't Everything" Brown
+-----------------------------+
| Razors pain you; |
| Rivers are damp; |
| Acids stain you; |
| And drugs cause cramp; |
| Guns aren't lawful; |
| Nooses give; |
| Gas smells awful; |
| You might as well live. |
| --Dorothy Parker |
+-----------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

"Jesse Falsone" wrote:

I have been gravitating toward larger tires on my road bike - going from
23s to 25's, and I've just ordered some 28's.

Good move. I've also gone from 23s to 25s (labelled as 28s).

I've been generally
trying to use the smallest tube for a given tire. Does anyone know if
I can use a tube rated for 18-25mm on a 28? All tires and tubes in
question are Contis (tires are Ultra 2000).

Yes you can, but since the tube will be stretched more, it will tend to lose
air faster in between fillups, and may be more likely to puncture. I tend to
use the largest tube that will fit comfortably in the tire.

Also, I'm a bit concerned with tire clearance on my bike frames. I
don't have much with 25's right now (tire to seat tube in back and tire
to fork), and in theory, the 28's should have a larger diameter. I
guess I'll find out for sure when I get the tires, but I was wondering
if this diameter varies a lot (I would have to think it does vary
some).

It does vary somewhat for a given width tire (based on the thickness of the
tread). You also have to watch the clearance to the brake calipers and chain
stays.

Art Harris

On Wed, 29 Dec 2004 03:33:23 +1100, Jesse Falsone
wrote:


I have been gravitating toward larger tires on my road bike - going from
23s to 25's, and I've just ordered some 28's. I've been generally
trying to use the smallest tube for a given tire. Does anyone know if
I can use a tube rated for 18-25mm on a 28? All tires and tubes in
question are Contis (tires are Ultra 2000).

Also, I'm a bit concerned with tire clearance on my bike frames. I
don't have much with 25's right now (tire to seat tube in back and tire
to fork), and in theory, the 28's should have a larger diameter. I
guess I'll find out for sure when I get the tires, but I was wondering
if this diameter varies a lot (I would have to think it does vary
some).

If there's something I've learned during years of changing tire sizes
over various bikes, it's that the numerical tire size is sort of a
suggestion. Example, a Hutchinson Carbon Comp 700x23 has exactly the
same diameter as a Michelin Axial Pro 700x20. I've found similar
inconsistencies with touring tires while mixing and matching
Panaracers, Conti Gator Skins, Michelin Tracers, and Specialized
Turbos.

Basically when we're talking about frame clearance it's really a "suck
and see" proposition.

BTW, I've never hesitated in using tubes designated for use with
smaller tires in touring size tires.


jeverett3ATearthlinkDOTnet http://home.earthlink.net/~jeverett3

On Wed, 29 Dec 2004 03:33:23 +1100, Jesse Falsone wrote:

Also, I'm a bit concerned with tire clearance on my bike frames. I
don't have much with 25's right now (tire to seat tube in back and tire
to fork), and in theory, the 28's should have a larger diameter. I
guess I'll find out for sure when I get the tires, but I was wondering
if this diameter varies a lot (I would have to think it does vary
some).

If you are talking about the same brand and model, only a wider size, then
you reasonably can expect a 3mm width difference between the tires. This
will be a bit less than 3mm added radius to the wheel (since it is not a
complete circle around the tire between the beads), but close enough.

Going from one brand to another the meaning of the width varies greatly.

--

David L. Johnson

__o | Arguing with an engineer is like mud wrestling with a pig... You
_`\(,_ | soon find out the pig likes it!
(_)/ (_) |

Jesse Falsone wrote:

I have been gravitating toward larger tires on my road bike - going from
23s to 25's, and I've just ordered some 28's. I've been generally
trying to use the smallest tube for a given tire. Does anyone know if
I can use a tube rated for 18-25mm on a 28? All tires and tubes in
question are Contis (tires are Ultra 2000).

I used to use the British 24 x 1 3/8" tubes (ETRTO 540mm) in MTB tyres,
because they were cheap and just as light as the expensive superlight
butyl tubes in the proper ETRTO 559mm size, and the few mm difference in
diameter is irrelevant with an inflated tube. With the gradual
extinction of juvenile road bikes in favour of crappy 40lb full-sus
"ATBs", this tube size is rarely available so I now use proper MTB tubes.

I had no punctures riding with these overstretched tubes, except for a
single 40-mile ride when I had five holes, all in different places.
Must have been hedge-cutting season.

On 12/28/2004 11:33 AM, Jesse Falsone wrote:
I have been gravitating toward larger tires on my road bike - going from
23s to 25's, and I've just ordered some 28's. I've been generally
trying to use the smallest tube for a given tire. Does anyone know if
I can use a tube rated for 18-25mm on a 28? All tires and tubes in
question are Contis (tires are Ultra 2000).

Also, I'm a bit concerned with tire clearance on my bike frames. I
don't have much with 25's right now (tire to seat tube in back and tire
to fork), and in theory, the 28's should have a larger diameter. I
guess I'll find out for sure when I get the tires, but I was wondering
if this diameter varies a lot (I would have to think it does vary
some).



Officially, you obtain the tire width rating by spreading the tire out
flat and measuring the overall width and dividing by 2.5. So tall tires
would end up with a falsely wide rating. That's why tires of the same
rating have different actual inflated widths.

--
Tom Reingold
Noo Joizy

i never noticed the leaking stuff nor more flats but found that an
undersized tube is more likely to rupture/split when punctured.
i never use a tube more then one size smaller then the tire. i
would not use a '18-25' in a 28 since it would be more 18 than a 25.